Travis: before_script added tracing

Added some echo statements and separators in the output to make it
easier to see in the logs where things went wrong in case of failure.
Travis: before_script exit 1 in case of errors
Travis: branch spec switch from white- to blacklist

Instead of only building master and master-1.2.x, we now build all
branches except master-2.0.x.

This allows users who fork the main repo and create feature branches
have them go through the build process